GIS and The GeoSciences Summer Institute

Landslide Analysis

1. Creating a location map and adding data.

You have collected a set of data on landslides in the Portland metropolitan area and need to produce a location map and do a visual analysis of the landslide intensity. You will find basic basemap materials in the ESRI data set, and use this landslide file to plot the distribution and volume of landslides resulting from the 96/97 storm event. Here is a copy of the report that accompanied the data set.

 

  1. Download the data file.
  2. Open landslides.xls in Excel.
  3. Export the data as a Tab Delimited file (from the File->Save As dialog box).
  4. Open ArcView and create a new View.
  5. From the Tables section of the Project Manager, Add the file you just created in Excel.
  6. With a View active, From the View menu, choose Add Event Theme, and choose which fields to use as X and Y coordinates.
  7. Add the States and Counties themes from the C:\Esri\Esridata\US directory.
  8. Redefine the Counties theme to show just Oregon counties (use the theme query!)
    • Activate counties
    • Theme->Properties
    • Click the Hammer (Query Builder)
    • Dbl-click State_name, click =, Dbl-click Oregon (see fig below)
    • Force a refresh by dbl-clicking the legend and choosing State_name from the Values field.
  9. Create a new shapefile of just the counties where landslides are plotted (select by theme tool)
    • Make the Counties theme active in the legend (raised up looking)
    • Choose Theme->Select By Theme
    • The first drop down box (implicitly, this is the "Relationship" field) should be Intersect, the 2nd (implicitly "Is related to") should be the landslides theme. (see figure below)
    • Now you should have 4 counties highlighted in yellow, they ar the ones that matched your query. Choose Theme->Convert to shapefile and give it a new name like "counties_with_landslides". This creates a new theme (coverage, layer, shapefile: all synonyms) of just the selected counties.
  10. Use Graduated Symbols to show which landslides had the largest volumes. Is it too busy? Try changing colors and symbols.
  11. Redefine the landslides theme to show just large landslides. (same basic steps as in 8 above, just type a number in, instead of choosing a value from the left). You can choose whether to use this or the entire set of landslides in your final map.
  12. Create a second View that has a zoomed out view of the whole state with the counties that have landslides mapped in them. Use Edit->Copy (or Cut) and Edit->Paste to move Themes (coverages, layers, shapefiles...) from one View to another.
  13. Create a Layout showing landslide volumes resulting from the 1996/97 storm events.
    • With the View active choose View->Layout, and select the Landscape-Inset template. Show Oregon, and then a zoomed in view of the study area. Print it!

2. Basic analysis: How many landslides in each geologic type

  1. Add the geologic map data. (unit descriptions) (clipped_and zipped)
  2. Spatial join the geology data to the landslide table. (remember to select the shape field)
    • Use Open Theme Table to gain access to the underlying tables of both NewGeol_clip_dd and Landslides_dd
    • Click on the Shape field in each
    • With the Landslides table active, Click the Join button, or chooseTable->Join. This will join the attributes of the geologic bedrock that each landslide is sitting on to the landslide RECORD, which will ATTRIBUTE each landslide with the Geology (Ptype) it occured on.
  3. Find the average volume and number of landslides for each type of geology.
    • With the Landslides table active, click on the Ptype (or Code, if you used geology instead of newgeol) field.
    • Either click the Sigma button, or choose Field->Summarize
    • Select the volume (or any other numeric field you are intesrested in) field and choose Average (note that I also chose StDev)
  4. Make a chart of count vs Ptype.
    • Click Ptype (or Code)
    • Click the Create Chart button, or choose Table->Chart
    • Highlight fields on the right that you want to graph, and click add. (Note, you have way more control in Excel!)
    • Which Geologic types had the most slides (count)? The largest average volumes?
  5. If you have time, make a chart of area vs Ptype. What does this tell you about the distribution of landslides?

3. Downloading and converting the base data that you just used

  1. Download the geology data from Oregon GIS Service Be sure to read the information about the data format! To illustrate the difference in file formats, get at least one data set in ArcInfo format. You will need to Convert to shapefile before you can re-project it!

    Heres are some other sites that have useful data in various formats:

    Metro

    NW GeoData Clearinghouse

    US Geological Survey

    US Census

    Geospatial Clearinghouse Network

    GIS Data Depot

  2. Load the Projection Utility Wizard extension..
  3. Project the landslide counties theme (from part 1) into the special Oregon Lambert projection.
    • Choose File->ArcView Projection Utility
    • Wait while it initializes...
    • Choose the Theme that you want to Reproject (counties_with_landslides?)
    • Choose GCS_North_American_1983
    • Click next
    • Answer "Yes" to saving the coordinate system information
    • Select NAD_1983_Oregon_North, and Feet! This is a good place to start for our Custom Projection, because the parameters are mostly the same...
    • Click the Parameters tab
    • Change the False Easting field to: 1312335.958, the Central Parallel Field to 41.75 (remember your decimal degrees?), Standard_Parallel_1 to: 43, Standard_Parallel_2 to: 45.5
    • Click Next, Click Browse on the next screen and give the new file a name that reflects its projection, like "counties_ORSP". Be sure to verify what directory the new shapefile is going into so you can find it later.
    • Click Next again, and after a short wait, Click Finish
    • A progress bar will eventually pop up, wait patiently...
    • Eventually you will see a message that it has "Finished processing shapefiles". Click Ok. It will then ask if you want to add the shapefile. Say Yes.
  4. Load the Geoprocessing wizard extension.(File->Extensions)
  5. Use the theme you just created to clip just the geology for your area.
    • Choose View->Geoprocessing Wizard...
    • Choose the radio button Clip one theme based on another. Look at the other options to get an idea of what other things you can do! Cool, huh?
    • Choose the theme you are going to clip, and the theme you will clip it with. Give your output clipped file a name (like newgeol_clipped, so you can keep track of it!)
  6. Okay, now Project your clipped area back to Decimal Degrees.(just the oposite of the previous projecting steps!)